Electric vehicle
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| Transmission lines 765, 500, 345, 230, and 138 kV Figure 4.1 Electricity grid in North America. (Source US DOE, http://en.wikipedia.org/wiki /Electric_power_transmission.) Figure 4.2 Renewable electricity superhighways (Source http://en.wikipedia.org/wiki/High-vol tage_direct_current) 4.2 Infrastructure Needed for Charging Electric Vehicles Once electricity has been transmitted to the point of use it has to be supplied to the EVs which will use it. Most buildings in the developed world have electrical sockets available which will typically supply up to 3 kW of power and hence the assumption is that EVs can be charged overnight ready for the next day or during the day while parked at work. For more rapid charging, sockets which transmit greater amounts of power combined with appropriate cabling need to be available. The Nissan Leaf, for example, has a battery capacity of 24 kWh and if this is to recharge 80% of its capacity in 48 minutes then kW of power will need to be available at the socket. For home charging such sockets will need to be fitted. Charging at work will need to be catered for with appropriate sockets being available in the work car park, in public car parks or for street parking. Electricity Supply 81 Inductive charging points are another option and these need to be wired in where the vehicle is parked. Motorway service stations are an interesting example. While it is too early to predict a demand pattern it is not unreasonable to consider cars per hour needing a rapid charge. A hundred charging points each supplying 24 kW will create a demand for 2.4 MW. Clearly, considerable planning needs to be done on the likely infrastructure if battery EVs become common. 4.3 Electricity Supply Rails Electric trains normally take power from supply rails or overhead supply lines. These can either be DC or AC lines. For example, London Underground trains run on DC supply rails the rail besides the track runs at 420 V and the central rail runs at 210 VAC supply can be either single phase or multiphase. The train takes electric current from a rail or wire mounted on insulators. The current is collected from steel shoes which are in contact with the supply rail running parallel to the track. The shoes which are connected to the train move as the train moves. Alternatively, the current can be collected from overhead lines. The supply rails normally use direct current. There is a choice between using a three- rail or a four-rail system. In the three-rail system the rail runs at several hundred volts and the current is returned via the normal running rails. In the four-rail system as used on the London Underground the current is returned through the fourth rail. The most common DC voltages are 600 and 750 V for trams and underground trains of metros and, 650/750 V third rail for the former Southern Region in Britain, and 3 kV overhead. The lower voltages are often used with third- or fourth-rail systems, whereas voltages above 1 kV are normally limited to overhead wiring for safety reasons. A pickup fora DC third rail is illustrated in Figure 4.3. Most third-rail systems are used with a DC supply. Overhead systems are used with either DC or AC supply. The Tyne and Wear Figure 4.3 Third-rail contact shoe of Chicago L car. (Source: http://en.wikipedia.org/wiki/ Third_rail.) |